It is becoming apparent that, in the future, lithium-ion battery systems which are subject to very stringent requirements in respect of reliability, safety, performance and life, will be used both in stationary applications, for example in wind turbines, in vehicles, for example in hybrid and electric vehicles, and in laptops and mobile telephones.
The principle functional design of a battery system in accordance with the prior art is shown in FIG. 1. In order to achieve the required performance and energy data with such a battery system, individual battery cells 100 are usually connected to one another in series and sometimes additionally in parallel with a battery. A group of battery cells 100 is in this case connected in each case to one of a plurality of battery cell supervision units 102, also referred to as cell supervision circuit or CSC. A further functional unit is formed by the battery management system 104, to which the battery cell supervision units 102 are connected. In this case, the battery management system 104 ensures a high degree of safety, performance and life of the battery system. In addition to a battery state identification, said battery management system also includes diagnosis and safety functions and communications interfaces for other systems, for example thermal management of the battery.
A battery isolation unit 106, which is arranged between the battery cells 100 and terminals of the battery system, performs, inter alia, connection and disconnection of the battery to and from consumers. The battery isolation unit 106 is controlled by the battery management system 104 and safeguards the battery system with respect to impermissibly high currents and voltages and provides safety functions such as, for example, two-terminal disconnection of the battery cells 100 from the battery terminals, for example during maintenance work on the battery system. In conventional battery management systems, generally all-encompassing reserves or safety margins are nowadays included in the calculation for this in order to not pose a risk to the safety of the battery system which needs to be maintained with the greatest degree of priority for reasons of the provision of an excessively high performance.
The function of a conventional battery cell supervision unit 102 is shown in FIG. 2. The battery cell supervision unit 102 comprises, in a known manner, an analog-to-digital converter 200, which is connected to one of the battery cells 100 via a filter circuit 202. The analog-to-digital converter 200 digitizes a battery cell instantaneous voltage of the battery cell 100 and makes this available to evaluation electronics 204. The evaluation electronics 204 can then provide a control signal for a state-of-charge balancing circuit 206, also referred to as cell balancing, which is connected in parallel with the battery cell 100. In order to ensure safe operation of the battery cell 100, a comparator 208 is often also connected in parallel with said battery cell. Since it is known that conventional lithium-ion battery cells 100 have an operating voltage of typically 2.8 volts to 4.2 volts, the comparator 208 is configured such that it generates an alarm signal on an alarm signal bus 210 in the event of the lower or upper operating voltage being undershot or exceeded.
The measuring of the battery cell voltage, firstly by the battery cell supervision unit 102 and secondly by the comparator 208, therefore nowadays already ensures comparatively reliable supervision of battery cells 100.